The present invention relates generally to methods for finding faults on electrical transmission lines, and more particularly to a method for finding a fault on an electrical transmission line, in which a pulse is applied to one end of the transmission line and a reflected signal is detected at the same end.
Bindlingmaier, A. Haag and K. Kuhnemann "Einheiten, Grundbegriffe, Messverfahren der Nachrichten-Ubertragungstechnik" [Units, Fundamental Terminology, Measurement Methods for Telecommunications Transmission Technology], Siemens Akiiengesellschaft, Issue November 1969, pages 80 and 81, discloses a method for detecting a fault on an electrical transmission line, in which the time difference between a transmitted pulse and its echo signal is measured in order to deduce from this the position of a line fault. The significance and type of the fault can be found from the magnitude and form of the echo signal with respect to the corresponding parameters of the transmitted signal. However, the known method is suitable only for determining faults which are not located too far from the point at which the transmitted signal is fed in, but is not suitable for determining remotely located line faults, because the echo signal is lost in the noise in the case of faults located at long ranges. In addition, in the case of the known method, the profile, which is visible on the screen of an oscilloscope, of the transmitted signal and echo signal must be interpreted, with respect to faults, by a person skilled in the art.
U.S. Pat. No. 4,041,381 discloses a method for finding a fault on an electrical line in which a digital signal is repeatedly applied to the line to be investigated, which digital signal has the property that its autocorrelation function is a pulse function and the digital signals reflected on the line are received. In addition, in the case of the known method, further digital signals, which are similar to the first digital signals, are produced repeatedly and are progressively delayed. The delayed digital signals and the reflected signals are multiplied by one another, and the multiplication result is integrated. The range of the fault point giving rise to the reflection on the line is found from the peak value of the integration result.
DE 24 04 233 A1 discloses a method for the localization of fault points in the insulation of insulated conductors, in which method the autocorrelation function is found for a signal mixture arriving at one conductor end, but the signal mixture comprises interference-discharge and partial-discharge pulses. The partial-discharge pulses are produced at fault points in the insulation of the conductor when a sufficiently high AC voltage is applied and partial discharges occur there. The position of the fault points is deduced from the partial-discharge pulses detected at the conductor end. A precondition of this is that the partial-discharge pulses, which are scarcely raised above the level of the interference, can also actually be detected; the autocorrelation is used for this purpose.
The present invention is directed to the problem of developing a method for finding a fault on an electrical transmission line, which method considerably simplifies the detection and finding of faults as well as enabling the finding of faults occurring at a relatively long distance from the feed end.